Pacific Giant Salamanders in Mack Creek

Introduction

Beginning in 1993, researchers from the Andrews Experimental Forest Long-Term Ecological Research (LTER) have been monitoring populations of Pacific Giant Salamanders, Dicamptodon tenebrosus, specifically in Mack Creek (Gregory 2016). The Experimental Forest is part of the Willamette National Forest in western Oregon and managed by the U.S. Forest Service and Oregon State University (Figure 2.). Researchers are interested in how disturbances in forests effect biota. The data was collected from two sections of of Mack Creek - a clear cut section and an old-growth section. Here, we will use the data collected by the Andrews Experimental Forest Team to compare the differences in size and weight distributions of salamanders from clear cut and old growth sections.

Figure 1. A Pacific Giant Salamander (Dicamptodon tenebrosus) laying on a down log. Photo credit: Gary Nafis, www.californiaherps.com.

Figure 2. Map of HJ Andrews Experimental Forest LTER in Oregon. Andrews Experimental Forest is managed by the U.S. Forest Service and Oregon State University. Map courtesty of: HJ Andrews Experimental Forest.

Data and Methods

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Results

Results A: Annual salamander counts in old growth and clear cut sections of Mack Creek

Salamander counts in old growth and clear cut sections were compared between 1993 and 2017. Overall, salamander counts in both sections followed similar patterns; when counts in old-growth sections were high (>200), counts in clear cut sections were also high. Similarly, when counts of salamanders in old-growth sections were low (<200), salamander counts in clear cut sections were also low. In 1994, 2011, and 2015-2017, salamander counts were higher in clear cut sections than old growth sections. In total, old growth sections had higher counts of salamanders (n = 5,951) compared to clear cut sections (n = 5,051) over the 17 year period.

Figure 3. Salamander counts in clear cut (orange) and old growth (green) sections of Mack Creek. Old growth sections are responsible for higher counts of salamanders for 80% of the time between 1993 and 2017. The populations in both sections display similar patterns of highs and lows. Data: Stanley Gregory, Andrews Forest LTER Sites.

Results B: Table of 2017 salamander counts by channel classification

Table 1. Salamander counts in different channels of clear cut and old-growth forests: cascade, pool, and side channel. Data: Stanley Gregory, Andrews Forest LTER Sites.

Channel Type	Clear Cut Forest	Old-Growth Forest
Cascade	247 (55.1%)	201 (44.9%)
Pool	31 (40.8%)	45 (59.2%)
Side Channel	90 (54.9%)	74 (45.1%)

Salamander counts in clear cut sections were higher in cascades (n_cascade = 247 (55.1%)) and side channels (n_sidechannel = 90 (54.9%)). In old-growth sections, pools had higher counts of salamanders (n_pool = 45 (59.2%)).

Results C: Is there a significant difference in salamander counts in channel locations in old growth and clear cut forests?

We performed a Pearson’s Chi-squared test to examine whether or not there was a significant difference in where in the channel Pacific giant salamanders are located between the two sections of forest (ol-growth and clear cut). The results from our test found a that there was no siginificant difference in what channel Pacific giant salamander are located in between old growth and clear cut forests (\(\chi\)²(2) = 5.54, p > 0.001).

Results D: Is there a significant difference in mean weights for salamanders observed in clear cut vs old growth forests in 2017?

double check wording of the data spread conclusion to labs we’ve done with allison

Results E: Is there a significant difference between mean salamander weights in the 3 channel types of Mack Creek in 2017?

Salamanders found in side channels of Mack Creek had the lowest mean weight (mean₂₀₁₇ = 5.68 grams) compared to salamanders found in pools (mean₂₀₁₇ = 9.30 grams) and cascades (mean₂₀₁₇ = 7.52) (Figure 4.).

Figure 4. Weights of salamanders in cascade, pool, and side channels of Mack Creek. Mean weights for each channel type are indicated by the black center dot. Standard error of weights are indicated by the upper and lower bars. Data: Stanley Gregory, Andrews Forest LTER Sites.

Summary

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References

HJ Andrews Experimental Forest Long Term-Ecological Research. https://andrewsforest.oregonstate.edu/sites/default/files/lter/data/map/2011base.jpg

Gregory S. V. 2016. Aquatic Vertebrate Population Study in Mack Creek, Andrews Experimental Forest, 1987 to present. Environmental Data Initiative. https://doi.org/10.6073/pasta/5de64af9c11579266ef20da2ff32f702. Dataset accessed 11/25/2019.

Nafis, Gary. “Great Pacific Salamander.” CaliforniaHerps. http://www.californiaherps.com/salamanders/pages/d.tenebrosus.html